Since optical discs such as CDs (Compact Discs) and CD-ROMs (Compact Disc Read Only Memories) are easy to handle and their production costs are relatively low, as recording mediums for storing data, they have been widely used. In recent years, CD-R (Compact Disc Recordable) discs, which are data write-once type discs, and CD-RW (Compact Disc ReWritable) discs, which are data rewritable type discs, have come out. Thus, data can be easily recorded on such optical discs. Optical discs such as CD-DA (Compact Disc Digital Audio) discs, CD-ROM discs, CD-R discs, and CD-RW discs based on the CD standard have become the mainstream of data recording mediums. In recent years, moreover, content data such as audio data compressed according to MP3 (MPEG 1 Audio Layer-3) and ATRAC (Adaptive TRansform Acoustic Coding) 3 have been recorded on CD-R discs, CD-RW discs, and so forth.
However, since CD-R discs and CD-RW discs have come out, data recorded on optical discs such as CD-DA discs and CD-ROM discs can be easily copied. Thus, data recorded on discs has been copied to other discs and illegally used. As a result, a problem of copyright protection has arisen. Thus, it is necessary to take countermeasures for copyright protection of content data.
As one method for protecting content data recorded on such an optical disc, the content data recorded on the disc is encrypted.
When content data recorded on a disc has been encrypted, unless key data with which the content data is decrypted is obtained, the content data cannot be decrypted. Thus, the content data can be protected. A system that uses DRM (Digital Rights Management) data as information about copyright protection of content data to restrict reproducing operation and copy operation of the content data may be considered.
However, when content data is encrypted to protect copyright of content data, the recording position of key data thereof should be considered. To strongly protect content data, it is preferred to record the key data at a position that a conventional player and a conventional drive cannot easily access. As such a position that the conventional player the conventional drive cannot easily access, there would be for example a lead-in area, a lead-out area, or the like of a disc.
However, when key data with which content data is decrypted is recorded at a position such as a lead-in area, a lead-out area, or the like-that cannot be easily accessed, the content data cannot be reproduced unless a new type player or a new type drive that can deal with it is used. Players and drives that can record and reproduce data to/from CD-DA discs, CD-ROM discs, CD-R discs, and CD-RW discs have been widely used. Thus, in consideration of compatibility with the conventional players and drives, the key data cannot be recorded at a position that they cannot easily access. Thus, the key data has to be recorded at a position such as a program area of a disc that they can relatively easily access.
However, when the key data is recoded in the program area, there will be a risk of which content data cannot be sufficiently protected. In particular, some of conventional CD-R drives and CD-RW drives have a disc copy function. Those drives can copy all data of one disc to another disc. With such a function, there is a possibility of which key data recorded in the program area is copied as it is.
Therefore, an object of the present invention is to provide a data recording medium, a data recording method and apparatus, and a data reproducing method and apparatus that prevent a disc from being copied so as to protect copyright of contents.